Altitude compensating ignition device



1948' w. c. PARRISH 2,441,284

ALTITUDE COMPENSATING IGNITIQ) DEVICE Filed Aug. 5, 1943 2 Sheets-Sheet 1 A 50 .2; 26 22 1a 4665A y 9 8 W. C. PARRISH 2 441 2 4 ALTITUDE COMPENSATING IGNITION DEVICE Filed Aug. 5, 1943, 2 Sheets-Sheet 2 wax- Patented May 11, 1948 ALTITUDE COMPENSATING IGNITION DEVICE WillianrC. Parrish, Park Ridge, lll., assignor to Stewart-Warner Corporation, Chicago, Ill., a corporation of Virginia Application August 5, 1943, Serial No. 497,476

4.Claims. 1

My invention relates to altitude compensating ignition devices more particularly adapted for, but not limited to, use in connection with the internal combustion heaters of aircraft.

It is now common practice to provide aircraft with internal combustion heaters to provide heated ventilating air for cabins and other enclosed spaces. In most types of internal combustion heaters used for this purpose, the combustion chamber of the heater is maintained at a pressure differing only slightly from atmospheric pressure. Where a spark plug is used to ignite the combustible mixture delivered to the combustion chamber, it has been found that when the aircraft reaches an altitude above 20,000 or 25,000 feet, the spark plug produces a corona effect but does not provide a spark capable of igniting the combustible mixture.

An object of my invention is to provide a spark plug or similar ignition device which is automatically compensated for variations in atmospheric pressure and which is effective to produce. at all altitudes, a spark capable of igniting a combustible mixture.

Another object of my invention is to provide an altitude compensating ignition device wherein the spark producing electrodes are protected against the increased burning effect resulting from lowered gap resistance .due to increased altitudes.

Another object of my invention is to provide an altitude compensated ignition device which is inexpensive to manufacture, simple to install, and capable of providing long and trouble-free service.

Another object of my invention is to provide an altitude compensating ignition device which may be easily disassembled for purposes of inspection and repair.

Other objects of my invention will become apparent as the description proceeds.

In the drawings:

Fig. 1 is a sectional view showing a unitary spark plug embodying my invention. This plug is shown attached to the wall of a combustion chamber;

Fig. 2 is a sectional view showing a modified form of my invention applied to a combustion chamber; I

Figs. 3 and 4 are transverse sections taken on the lines 3-3 and 44, respectively, of Fig. 2;

Fig. 5 is a sectional view showing a third form of my invention applied to a combustion chamber; and

Fig. 6 is a top plan view of the form of my invention shown in Fig. 5.

In Fig. 1, I have shown, at approximately twice normal size, an embodiment of my invention which assumes the form of an ordinary spark plug and may be used in lieu thereof. In this figure I have illustrated a combustion chamber ill of an internal combustion heater of the kind commonly used in aircraft. This heater may be like that shown in my co-pending application, Serial No. 494,155, filed July 10, 1943, or of any other suitable type. The wall of the combustion chamber is threaded, as indicated at l2, to receive a spark plug of conventional form or of the particular type disclosed and claimed in this application.

My altitude compensating ignition device in this instance takes the form of a spark plug having a sleeve ll threaded at the lefthand end to cooperate with the conventional threads l2 of the spark plug receiving opening of the combustion chamber III. A conventional gasket I6 is provided in accordance with usual practice to seal the joint between the spark plug and the wall of the combustion chamber. The sleeve [4 is provided with a fixed electrode l8 which is grounded through the sleeve and wall of the combustion chamber. A second or movable electrode 20 is formed by the bent over end of a wire22 mounted in a porcelain sleeve 24 and secured in proper position therein by lock nuts 26 engaging threads provided on the righthand end of the wire 22. This wire may be of uniform composition throughout, or the bent over end 20 may be coated. or of different material from the rest of the wire to provide an eflicient electrode while at the same time the righthand end of the wire is of sufficient strength to carry out the functions hereinafter described.

A tubular guide 28, having in-turned ends 30 and 32, is press fitted or otherwise secured in the metal sleeve il in the position shown in Fig. 1. The wire 22 and porcelain sleeve 24 are slidably mounted in this guide and the porcelain sleeve 24 is preferably covered with a metal skirt 34 which moves with the porcelain sleeve and has direct sliding contact with the in-turned end of the guide 28. The skirt 3 and porcelain sleeve 24 have engaging shoulders 35 and 38, respectively, and leftward movement of the electrode 20 is limited by engagement of the shoulder 38 with the end 32 of the guide 28.

A sheet metal shell 40 is welded or soldered to an annular base 42 screwed to the righthand end of the metal sleeve I. An evacuated metal lfllIlIi-VS or sylphon 44 is located in the shell 40 and a porcelain liner 46 prevents electricity from jumping between the sylphon 44 and the shell 40. The sylphon 44 contains a coil spring 46 which acts against atmospheric pressure to exband this sylphon lengthwise. A nut 50 is soldered to the lefthand end of the sylphon 44 and is threaded to receive the threaded end of wire 22. A look nut 62 is provided to prevent rota- Lion of the wire 22 in the nut 50 when subjected to severe vibration.

The righthand end of the sylphon 44 is soldered to the head of a bolt 54. This bolt passes through a metal washer 56, an insulating washer 66, in insulating cap 60, a second metal washer 62, and the opening in an electrical terminal 64. Nuts 66 clamp the terminal 64 in place and also maintain the several parts in the assembled position shown in Fig. l. A wire 66 connects the terminal 64 with any suitable source of electrical current and the insulating washer 58 and cap 60 prevent grounding of this terminal through the shell 46.

A series of openings III are provided in the shell 40. and porcelain liner 46. The purpose of these openings is to maintain atmospheric pressure in the chamber 12 surrounding the sylphon or bellows 44 so that the pressure in this chamber will vary with variations in atmospheric pressure as the aircraft increases or decreases its altitude. As the pressure decreases in the chamber I2, bellows 44 expands and moves wire 22, porcelain sleeve 24 and skirt 34 to the left, as viewed in Fig. l. tween the electrodes l8 and 20, whereby the resistance of this gap is maintained substantially constant. As the aircraft loses altitude, the pressure increases in the chamber '12, causing a contraction of the bellows 44 with a resulting closing of the gap between the electrodes I8 and 20.

When my novel spark plug is initially assembled, the righthand end of the wire 22 is screwed into the nut 50 an appropriate distance to give the desired gap between the electrodes I8 and 20. If the electrodes become burned away, the proper gap can be reestablished -by unscrewing nuts 66 from bolt 54 and then unscrewing base 42 from the righthand end of metal sleeve I4 to expose nuts 50 and 52 for appropriate adjustment. If electrode 20 should become unsuitable for further use, the wire 22 may be removed from the porcelain sleeve 24 and a new wire substituted therefor.

The embodiment of Fig. 1 is simple and compact and forms a unitary structure which can be utilized to replace the conventional spark plug. My invention, however, is not limited to such a unitary construction and in Figs. 2 to 6, inclusive, I have shown other forms of my invention in which this unitary structure is dispensed with.

In the embodiment of Figs. 2 to 4, inclusive, the combustion chamber I is provided with a pocket I02 which communicates with the interior of the combustionchamber. In this form of my invention the fixed and movable electrodes I04 and I66, respectively, are located in this pocket. The fixed electrode is mounted in a porcelain sleeve I00 which insulates this electrode from the metal wall in which it is mounted and a suitable electrical conductor IIO connects this electrode with any suitable source of current. As best shown in Fig. 2, a threaded ring '2 is afllxed-by welding, or many other suitable manner-rte one wallet the pocket I02;

A metal sleeve II carrying the porcelain sleeve I08 and electrode I04 is positioned in the ring H2 and secured therein by a tubular nut II6. A conventional gasket IIB may 'be confined between an internal shoulder I20 provided by the ring H2 and an external flange I22 provided by This increases the gap bethe sleeve H4 to prevent leakage between the ring I2 and this sleeve.

A sheet metal housing, indicated generally by reference numeral I24, is welded or otherwise attached to a second wall of the pocket I02. This housing comprises a base I26 having a tubular extension I28 projecting into the pocket I02 and forming a guide for a movable electrode I06. The housing I24 also includes a cylindrical central portion I30 attached to the base I26 by screws I32 and a cap I34 secured to the other end of the central portion I30. The housing I24 provides an enclosure for an evacuated, spring loaded, expansible bellows I36. A pin I36 extends diametrically through the cylindrical housing I24 and through a bracket I40 attached to the lower end of the bellows I36 so that the pin I30 constitutes a support tor this bellows.

The upper end of the bellows abuts 'a plate I42 attached by bolts I44 to the upperend of an elongated cup I46. The movable electrode I06 has a reduced, threaded end I46 passing through an opening in the base I50 lot the cup I46 and secured to this base by nuts I62. -Pin I36 passes through slots I54 in the cup I46 whereby this cup is permitted to move with can pansion and contraction of the bellows I36. Plate I42 is of smaller diameter than the cylindrical section I30 of the housing I24 and" is slidably guided in this housing by inwardly pro- Jecting ribs I56. The interior of the housing I24, therefore, forms a single chamber I66 surrounding the bellows I36 and freely communicating with atmosphere by way of openings I60 in cap I34.

In this form of my invention the operation of the bellows is reversed in the sense that expansicn of this bellows causes movement of the movable electrode toward the fixed end of the bellows and contraction of the bellows causes movement of this electrode away from the fixed end of the bellows. The bellows, however, expands with decreases in atmospheric pressure to increase the gap between electrodes I04 and I06 and' contracts with increases inatmospheric pressure to decrease this gap,so' that the operation of this embodiment of my invention is generally the same as the operation of the embodiment shown in Fig. 1.

In the embodiment of Figs. 5 and 6, the combustion chamber 200 has a pocket 202 in open communication therewith. A fixed electrode 204 is carried in a porcelain "sleeve 206 and metal sleeve 208, which are mountedin a wall of the pocket 202 in the same-manner in which the corresponding parts of Fig. 2 are mounted in a wall of the pocket I02. An electricalconductor 2I0 connects the fixed electrode204 with any suitable source of current. I

A sheet metal base 2I2 is welded or otherwise secured to a second wall of the pocket 20!. The walls to which the base 2I2-and fixed electrode 204 are attached are preferably at right angles to each other. The base 2I2 supports a sleeve 2 having a tubular part extending down into the pocket 202. The sleeve .2I4 is clamped against the base 2I2 by clamps 2 I6 and 2 I6 which are screwed or otherwise secured to the base 2I2.

A tubular cap 220 is threadedly attached to the upper end of the sleeve 2.

The movable electrode 222 is rotatably mounted ii the sleeve 2 and has a bent over lower end 22! adjacent the inner end of fixed electrode 204 to provide an adjustable spark gap. The upper end of the electrode 222 is of reduced diameter and threaded as indicated at 226 to receive nuts 228 which secure a gear 230 to the upper end of this electrode in non-rotative relation thereto. A flange 232 is integral with a sleeve 234 confined between the gear 230 and an opposed shoulder provided by the electrode 222. This flange is located between sleeve 2M and cap 220 and limits longitudinal movement of the electrode 222 relative to sleeve 2 l4.

Gear 230 is driven by a segment gear 235 mounted on a pin 236 carried by a bracket 238 integral with the clamp- 2l6. Arm 240 has one end rigidly attached to the sector gear 235 and a second end pivotaily connected to a link 242 having its other end pivotally attached to the free end of a Bourdon tube 244. The fixed end of the Bourdon tube is soldered or otherwise secured to the bracket 238.

The Bourdon tube 244 will expand and increase its diameter with decreases in atmospheric pressure. This will produce a clockwise movement of sector gear 235 and a counter-clockwise movement of gear 230 and electrode 222. Such movement of the electrode will swing the lower end 224 away from alignment with fixed electrode 204, as indicated in Fig. 6 to thereby increase the gap between the electrodes. A subsequent increase in atmospheric pressure will partially or completely return the movable electrode to its original position, depending upon the extent of this increase.

From the foregoing description taken in connection with the accompanying drawings, it will be apparent that my invention may assume numerous forms and may be incorporated in either a single, unitary structure or form part of a larger assembly. Numerous other changes and variations may be made without departing from the scope of the invention and the particular embodiments shown are to be considered as illustrative only, as my invention includes all modifications, variations and equivalents coming within the scope of the appended claims. While I have described my invention as being particularly adapted for application to the combustion chamber of aircraft heaters, my invention is not limited to such use but may be utilized wherever varying pressure conditions make its use desirable or advantageous either to insure a. hot and efiective spark or to prevent undue burning of the electrodes.

I claim:

1. A sparkplug oi the class described, comprising a sleeve adapted to be secured to a wall a combustion chamber, a fixed electrode carried by said sleeve, a guide located in said sleeve, a movable electrode slidably mounted in said guide, a metal shell attached to the other end of said sleeve, said shell providing a chamber therein, an expansible bellows located in said chamber and adiustably connected to said movable electrode for shifting the same, an electrical terminal connected to one end of said bellows,

said bellows serving as a conductor for connectin: said terminal with said movable electrode, an insulating cup located in said shell, additional means for insulating said shell from said terminal, and means connectin: said chamber with atmosphere whereby the position of said movable terminal is varied with variations in atmospheric pressure.

2. A spark plug of the class described, comprising a sleeve adapted tobe secured to a wall of a combustion chamber, a fixed electrode carried by said sleeve, a guide located in said sleeve, a movable electrode siidably mounted in said guide, a shell attached to the other end of said sleeve, said shell providing a chamber therein, an expansible bellows located in said chamber and adjustably connected to said movable electrode for shifting the same, an electrical terminal connected to one end of said bellows, said bellows serving as a conductor for connecting said terminal with said movable electrode, and means connecting said chamber with atmosphere whereby the position of said movable terminal is varied with variations in atmospheric pressure.

3. A spark plug of the class described, comprising a sleeve adapted to be secured to a wall of a combustion chamber, a fixed electrode carried by said sleeve, a guide located in said sleeve, a movable electrode slidably mounted in said guide, a metal shell attached to the other end of said sleeve, said shell providing a chamber therein, pressure responsive means located in said chamber and connected to said movable electrode for shifting the same, an electrical terminal connected to one end of said bellows, said bellows serving as a conductor for connecting said terminal with said movable electrode, an insulating cup located in said shell, additional means for insulating said shell from said terminal, and means connecting said chamber with atmosphere whereby the position of said movable terminal is varied with variations in atmospheric pressure.

4. Ignition apparatus of the class described, for igniting a combustible mixture in a chamber subject to variations in atmospheric pressure, said apparatus comprising a fixed electrode, a movable electrode shiftable lengthwise to vary the gap between said fixed and movable electrodes, 9. housing providing a second chamber, a pressure responsive bellows located in said second chamber and attached to said movable eleetrode,'-.

a guide in which said movable electrode is slidably mounted, said guide and electrode substantially cutting ofi communication between said two chambers, and means providing a free communication between said second chamber and atmosphere.

WILLIAM C. PARRISH.

REFERENCES crran The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,208,926 Dick et al. Dec. 19, 1918 1,493,033 Gregg May 6, 1924 1,565,274 Hawley Dec. 15, 1925 1,898,691 Schafer Feb. 21, 1933 2,031,293 Wamellnk Feb. 18, 1928 2,117,211 Reutter May), 1938 2,297,386 Bielitz Sept. 29, 1942 2,340,734 Clark Feb. 1, 1944 2,352,411 Sandretto June 27,. 1944 FOREIGN PATENTS Number Country Date 315,151 Germany Oct. 30, 1919 

